1. Field of the Invention
The present invention relates to wireless communication technologies. More particularly, the present invention relates to a handover method that supports terminal mobility.
2. Background of the Invention
FIG. 1 is a diagram illustrating a System Architecture Evolution (SAE) system architecture of the related art. Specifically, User Equipment (UE) 101 is a terminal device for receiving data. An Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 102 is a wireless access network, in which a macro base station evolved Node B (eNB) that provides the UE with an interface for accessing a wireless network is included. A Mobile Management Entity (MME) 103 is responsible for managing a mobile context, a session context, and security information of the UE. A Serving Gateway (SGW) 104 mainly provides a user-plane function, and the MME 103 and the SGW 104 may be located at the same physical entity. A Packet Data Network Gateway (PGW) 105 is responsible for a function such as charging, lawful interception, and the like, and can also be located at the same physical entity as the SGW 104. A Policy and Charging Rules Function (PCRF) entity 106 provides a Quality of Service (QoS) policy and a charging rule. A Serving General Packet Radio Service (GPRS) Support Node (SGSN) 108 is a network node device for providing transmission of the data with routing in a Universal Mobile Telecommunication System (UMTS). A Home Subscriber Server (HSS) 109 is a home sub-system of the UE, and is responsible for protecting user information including a current location of the UE, an address of a serving node, user security information, a packet data context of the UE, etc.
Along with an increased service data rate of the UE, an operator provides a new technique: Selected Internet Protocol (IP) Traffic Offload (SIPTO). That is, when accessing a particular service, the UE performs a handover to an access point closer to the wireless access network during movement, thus an investment cost of a transmission network is effectively reduced, and the high data rate is provided with a better service experience.
It is proposed in the 3rd Generation Partnership Project (3GPP) that the network must support a capability of Local IP Access (LIPA) and the SIPTO. Specifically, in the SIPTO, when the UE accesses the Internet or another external network through a home enhanced based station (Home enhanced Node B, HeNB), a home base station (Home Node B, HNB), or the macro base station, the network can select or reselect a user-plane node much closer to the wireless access network for the UE. The LIPA means that the UE accesses a home network or an intranet through the HeNB or the HNB. When the LIPA is executed, the user-plane node close to the home base station can be selected or reselected, or the user-plane node located in an HeNB/HNB access network can be selected, for the UE. Specifically, the user-plane node can be a core network device or a gateway, and for the SAE system, it can be the SGW or the PGW or a Local Gateway (LGW), while for the UMTS, can be the SGSN or a Gateway GPRS Support Node (GGSN).
An existing handover procedure of the related art can be as shown in FIG. 2, and mainly includes the following steps.
At step 201, a source base station determines to perform a handover.
At step 202, the source base station sends a handover request to a source MME. In the handover request, target base station information, e.g. a target base station ID and a target Tracking Area ID (TAI), is included, and information such as a target Closed Subscriber Group (CSG) or a handover type can also be included.
At step 203, the source MME sends a forward handover request to a target MME. The target base station information obtained from the handover request and the like is included in the forward handover request.
At step 204, if the target MME reselects the SGW for the UE, a session establishment process is executed with the reselected target SGW. The Target MME sends a Session Establishment Request to a Target SGW, and the Target SGW sends a Session Establishment Reply to the Target MME.
If it is not required to reselect the SGW for the UE, there is no need to execute step 204.
At step 205, the target MME sends the handover request to a target base station.
At step 206, the target base station replies to the target MME with a handover request acknowledgement message.
At step 207, the target MME updates bearer information according to the target base station to which the UE performs the handover, which can specifically include requesting establishment of a user-plane tunnel between the target base station and the LGW.
In the existing handover procedure described above, the following situations may be presented.
First, a successful handover cannot be ensured when the handover is performed. For example, after the UE is moved, the target base station is not allowed to access the LGW currently accessed by the source base station. Or, when the UE performs the handover from an enterprise network to another network, the UE is not allowed to have such a handover, which may cause handover failure. However, in accordance with the existing handover procedure, the target MME can determine the handover failure and release a wireless resource having been established or occupied only during the user-plane tunnel establishment. Such a manner can occupy excessive signaling resources and wireless resources.
Second, when the handover is performed, although the handover can be successful, an optimal bearer cannot be ensured after the handover. For example, when the UE has the handover, the handover to outside of the enterprise network is performed. Although the policy of the operator allows having the handover, the bearer after the handover might not be the optimal bearer, which may cause network resources to not be used optimally.